Harvard Heart Letter

New wireless defibrillator approved

Under-the-skin device meets the needs of a special population.

Implantable cardioverter-defibrillators (ICDs) are personal devices designed to jump-start the heart, like shock paddles do. A traditional ICD has two parts. A pulse generator about the size of a deck of cards is implanted under the skin just below the collarbone. It contains a battery and computer software and stores an electrical charge. The pulse generator is connected to the heart by wire leads that are threaded into a vein leading into the heart. The leads constantly sense the heart's rhythm and can deliver a shock if necessary to restore a proper heart rhythm. The wires, however, can lead to infections and other problems.

In 2012, the FDA approved a wireless ICD called an S-ICD. "S" stands for subcutaneous, since the entire system is implanted under the skin. Like a traditional ICD, the S-ICD has a pulse generator that monitors the heart's rhythm and can deliver a shock. However, it is not connected to the heart by leads. Instead, it has a sensor that is placed under the skin along the breastbone in front of the heart. From that short distance, it can both monitor the heart's rhythm and deliver a shock when it's needed. This makes the S-ICD a good option for people at risk for an infection that could occur around the ICD leads in the heart, and for people with obstructed veins.

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